COLUMBIA GLACIER 283
may have had so low a surface that there was no tendency to overflow to the comparatively shallow side valley.
"The first case implies snow accumulation in the embayment a few decades ago at a rate not since maintained, and would correspond to a general expansion of glaciers followed in later decades by contraction; but the relations of the ice to the forest, to be described presently, show that such contraction has not taken place. The second case implies a general expansion of the glacier as the important element of its later history.
"Another medial moraine of the great ice field north of the nunatak passed just east of the nunatak and continued down the eastern arm of the glacier to its end, where it contributed toward the building of a great alluvial delta which was gradually obliterating one of the lakes."
In 1909 the band of clear ice between the east medial and the lateral moraine was narrower than ten years before, as if advance in midstream had crowded it over. The same thing seemed to be true of the whole broad east moraine below the junction of the medial and upper lateral moraines. Where it had been smooth in 1899, this broad lateral moraine was in 1909 severely crevassed throughout, and some debris had fallen into the crevasses; but the contact of clear and crevassed ice was as sharp as ever and the lateral moraine belt was narrower. We, therefore, infer lateral spreading of the area of clear ice in the interim. In 1910 this lateral spreading and crevassing had increased slightly, but there was only a little more white ice on this east side than the year before.
The moraine on the distributary east of the large nunatak, was slightly more extensive in 1909 than ten years before; but since snow covered it in June, 1910, we cannot tell its condition then. The apparent change from 1899 to 1909 may be due in part to more snow on this upper part of the glacier during Gilbert's June observation than at the time of our observations in August. This ice tongue is much less crevassed than the main glacier, although it has a steeper grade. It has scattered debris upon its eastern and terminal margins, less than in 1899, but the western side has a broad lateral moraine, apparently heavier than ten years ago, which seems to be made up partly of marginal debris from the large nunatak, but chiefly of material carried by a medial moraine from the main upper glacier. Near the northern end of the nunatak this medial moraine joins the lateral moraine, which had broadened and extended farther out into the ice in 1909 than ten years before. This extension is perhaps due to ablation near the warmer land.
On the western margin of the glacier we were unable to look far enough into the souther-most embayment to see whether the moraine still bends into it, as observed by Gilbert and shown upon his map. There seemed to be a marginal lake with icebergs on the northern side of this embayment in August, 1909. On June 80,1910, this lake had been drained, its site being marked by heaps of tumbled icebergs which had gone aground when the water was drained out beneath the main glacier.
In both this embayment and the one next north, the grade is so flat that it could not be determined from our remote viewpoint, whether the grade was reversed, as inferred by Gilbert, or whether these are debouchures of tributaries.
Still farther to the north and northeast the main glacier receives a number of accordant, hanging, and cascading glacier tributaries; but the absence of pronounced medial moraines away from the margins of the glacier indicates that though many of these are good-sized glaciers, they are all relatively small and unimportant compared with the main ice tongue.